*DECK CAIRY SUBROUTINE CAIRY (Z, ID, KODE, AI, NZ, IERR) C***BEGIN PROLOGUE CAIRY C***PURPOSE Compute the Airy function Ai(z) or its derivative dAi/dz C for complex argument z. A scaling option is available C to help avoid underflow and overflow. C***LIBRARY SLATEC C***CATEGORY C10D C***TYPE COMPLEX (CAIRY-C, ZAIRY-C) C***KEYWORDS AIRY FUNCTION, BESSEL FUNCTION OF ORDER ONE THIRD, C BESSEL FUNCTION OF ORDER TWO THIRDS C***AUTHOR Amos, D. E., (SNL) C***DESCRIPTION C C On KODE=1, CAIRY computes the complex Airy function Ai(z) C or its derivative dAi/dz on ID=0 or ID=1 respectively. On C KODE=2, a scaling option exp(zeta)*Ai(z) or exp(zeta)*dAi/dz C is provided to remove the exponential decay in -pi/31 and from power series when abs(z)<=1. C C In most complex variable computation, one must evaluate ele- C mentary functions. When the magnitude of Z is large, losses C of significance by argument reduction occur. Consequently, if C the magnitude of ZETA=(2/3)*Z**(3/2) exceeds U1=SQRT(0.5/UR), C then losses exceeding half precision are likely and an error C flag IERR=3 is triggered where UR=R1MACH(4)=UNIT ROUNDOFF. C Also, if the magnitude of ZETA is larger than U2=0.5/UR, then C all significance is lost and IERR=4. In order to use the INT C function, ZETA must be further restricted not to exceed C U3=I1MACH(9)=LARGEST INTEGER. Thus, the magnitude of ZETA C must be restricted by MIN(U2,U3). In IEEE arithmetic, U1,U2, C and U3 are approximately 2.0E+3, 4.2E+6, 2.1E+9 in single C precision and 4.7E+7, 2.3E+15, 2.1E+9 in double precision. C This makes U2 limiting is single precision and U3 limiting C in double precision. This means that the magnitude of Z C cannot exceed approximately 3.4E+4 in single precision and C 2.1E+6 in double precision. This also means that one can C expect to retain, in the worst cases on 32-bit machines, C no digits in single precision and only 6 digits in double C precision. C C The approximate relative error in the magnitude of a complex C Bessel function can be expressed as P*10**S where P=MAX(UNIT C ROUNDOFF,1.0E-18) is the nominal precision and 10**S repre- C sents the increase in error due to argument reduction in the C elementary functions. Here, S=MAX(1,ABS(LOG10(ABS(Z))), C ABS(LOG10(FNU))) approximately (i.e., S=MAX(1,ABS(EXPONENT OF C ABS(Z),ABS(EXPONENT OF FNU)) ). However, the phase angle may C have only absolute accuracy. This is most likely to occur C when one component (in magnitude) is larger than the other by C several orders of magnitude. If one component is 10**K larger C than the other, then one can expect only MAX(ABS(LOG10(P))-K, C 0) significant digits; or, stated another way, when K exceeds C the exponent of P, no significant digits remain in the smaller C component. However, the phase angle retains absolute accuracy C because, in complex arithmetic with precision P, the smaller C component will not (as a rule) decrease below P times the C magnitude of the larger component. In these extreme cases, C the principal phase angle is on the order of +P, -P, PI/2-P, C or -PI/2+P. C C***REFERENCES 1. M. Abramowitz and I. A. Stegun, Handbook of Mathe- C matical Functions, National Bureau of Standards C Applied Mathematics Series 55, U. S. Department C of Commerce, Tenth Printing (1972) or later. C 2. D. E. Amos, Computation of Bessel Functions of C Complex Argument and Large Order, Report SAND83-0643, C Sandia National Laboratories, Albuquerque, NM, May C 1983. C 3. D. E. Amos, A Subroutine Package for Bessel Functions C of a Complex Argument and Nonnegative Order, Report C SAND85-1018, Sandia National Laboratory, Albuquerque, C NM, May 1985. C 4. D. E. Amos, A portable package for Bessel functions C of a complex argument and nonnegative order, ACM C Transactions on Mathematical Software, 12 (September C 1986), pp. 265-273. C C***ROUTINES CALLED CACAI, CBKNU, I1MACH, R1MACH C***REVISION HISTORY (YYMMDD) C 830501 DATE WRITTEN C 890801 REVISION DATE from Version 3.2 C 910415 Prologue converted to Version 4.0 format. (BAB) C 920128 Category corrected. (WRB) C 920811 Prologue revised. (DWL) C***END PROLOGUE CAIRY COMPLEX AI, CONE, CSQ, CY, S1, S2, TRM1, TRM2, Z, ZTA, Z3 REAL AA, AD, AK, ALIM, ATRM, AZ, AZ3, BK, CK, COEF, C1, C2, DIG, * DK, D1, D2, ELIM, FID, FNU, RL, R1M5, SFAC, TOL, TTH, ZI, ZR, * Z3I, Z3R, R1MACH, BB, ALAZ INTEGER ID, IERR, IFLAG, K, KODE, K1, K2, MR, NN, NZ, I1MACH DIMENSION CY(1) DATA TTH, C1, C2, COEF /6.66666666666666667E-01, * 3.55028053887817240E-01,2.58819403792806799E-01, * 1.83776298473930683E-01/ DATA CONE / (1.0E0,0.0E0) / C***FIRST EXECUTABLE STATEMENT CAIRY IERR = 0 NZ=0 IF (ID.LT.0 .OR. ID.GT.1) IERR=1 IF (KODE.LT.1 .OR. KODE.GT.2) IERR=1 IF (IERR.NE.0) RETURN AZ = ABS(Z) TOL = MAX(R1MACH(4),1.0E-18) FID = ID IF (AZ.GT.1.0E0) GO TO 60 C----------------------------------------------------------------------- C POWER SERIES FOR ABS(Z).LE.1. C----------------------------------------------------------------------- S1 = CONE S2 = CONE IF (AZ.LT.TOL) GO TO 160 AA = AZ*AZ IF (AA.LT.TOL/AZ) GO TO 40 TRM1 = CONE TRM2 = CONE ATRM = 1.0E0 Z3 = Z*Z*Z AZ3 = AZ*AA AK = 2.0E0 + FID BK = 3.0E0 - FID - FID CK = 4.0E0 - FID DK = 3.0E0 + FID + FID D1 = AK*DK D2 = BK*CK AD = MIN(D1,D2) AK = 24.0E0 + 9.0E0*FID BK = 30.0E0 - 9.0E0*FID Z3R = REAL(Z3) Z3I = AIMAG(Z3) DO 30 K=1,25 TRM1 = TRM1*CMPLX(Z3R/D1,Z3I/D1) S1 = S1 + TRM1 TRM2 = TRM2*CMPLX(Z3R/D2,Z3I/D2) S2 = S2 + TRM2 ATRM = ATRM*AZ3/AD D1 = D1 + AK D2 = D2 + BK AD = MIN(D1,D2) IF (ATRM.LT.TOL*AD) GO TO 40 AK = AK + 18.0E0 BK = BK + 18.0E0 30 CONTINUE 40 CONTINUE IF (ID.EQ.1) GO TO 50 AI = S1*CMPLX(C1,0.0E0) - Z*S2*CMPLX(C2,0.0E0) IF (KODE.EQ.1) RETURN ZTA = Z*CSQRT(Z)*CMPLX(TTH,0.0E0) AI = AI*CEXP(ZTA) RETURN 50 CONTINUE AI = -S2*CMPLX(C2,0.0E0) IF (AZ.GT.TOL) AI = AI + Z*Z*S1*CMPLX(C1/(1.0E0+FID),0.0E0) IF (KODE.EQ.1) RETURN ZTA = Z*CSQRT(Z)*CMPLX(TTH,0.0E0) AI = AI*CEXP(ZTA) RETURN C----------------------------------------------------------------------- C CASE FOR ABS(Z).GT.1.0 C----------------------------------------------------------------------- 60 CONTINUE FNU = (1.0E0+FID)/3.0E0 C----------------------------------------------------------------------- C SET PARAMETERS RELATED TO MACHINE CONSTANTS. C TOL IS THE APPROXIMATE UNIT ROUNDOFF LIMITED TO 1.0E-18. C ELIM IS THE APPROXIMATE EXPONENTIAL OVER- AND UNDERFLOW LIMIT. C EXP(-ELIM).LT.EXP(-ALIM)=EXP(-ELIM)/TOL AND C EXP(ELIM).GT.EXP(ALIM)=EXP(ELIM)*TOL ARE INTERVALS NEAR C UNDERFLOW AND OVERFLOW LIMITS WHERE SCALED ARITHMETIC IS DONE. C RL IS THE LOWER BOUNDARY OF THE ASYMPTOTIC EXPANSION FOR LARGE Z. C DIG = NUMBER OF BASE 10 DIGITS IN TOL = 10**(-DIG). C----------------------------------------------------------------------- K1 = I1MACH(12) K2 = I1MACH(13) R1M5 = R1MACH(5) K = MIN(ABS(K1),ABS(K2)) ELIM = 2.303E0*(K*R1M5-3.0E0) K1 = I1MACH(11) - 1 AA = R1M5*K1 DIG = MIN(AA,18.0E0) AA = AA*2.303E0 ALIM = ELIM + MAX(-AA,-41.45E0) RL = 1.2E0*DIG + 3.0E0 ALAZ=ALOG(AZ) C----------------------------------------------------------------------- C TEST FOR RANGE C----------------------------------------------------------------------- AA=0.5E0/TOL BB=I1MACH(9)*0.5E0 AA=MIN(AA,BB) AA=AA**TTH IF (AZ.GT.AA) GO TO 260 AA=SQRT(AA) IF (AZ.GT.AA) IERR=3 CSQ=CSQRT(Z) ZTA=Z*CSQ*CMPLX(TTH,0.0E0) C----------------------------------------------------------------------- C RE(ZTA).LE.0 WHEN RE(Z).LT.0, ESPECIALLY WHEN IM(Z) IS SMALL C----------------------------------------------------------------------- IFLAG = 0 SFAC = 1.0E0 ZI = AIMAG(Z) ZR = REAL(Z) AK = AIMAG(ZTA) IF (ZR.GE.0.0E0) GO TO 70 BK = REAL(ZTA) CK = -ABS(BK) ZTA = CMPLX(CK,AK) 70 CONTINUE IF (ZI.NE.0.0E0) GO TO 80 IF (ZR.GT.0.0E0) GO TO 80 ZTA = CMPLX(0.0E0,AK) 80 CONTINUE AA = REAL(ZTA) IF (AA.GE.0.0E0 .AND. ZR.GT.0.0E0) GO TO 100 IF (KODE.EQ.2) GO TO 90 C----------------------------------------------------------------------- C OVERFLOW TEST C----------------------------------------------------------------------- IF (AA.GT.(-ALIM)) GO TO 90 AA = -AA + 0.25E0*ALAZ IFLAG = 1 SFAC = TOL IF (AA.GT.ELIM) GO TO 240 90 CONTINUE C----------------------------------------------------------------------- C CBKNU AND CACAI RETURN EXP(ZTA)*K(FNU,ZTA) ON KODE=2 C----------------------------------------------------------------------- MR = 1 IF (ZI.LT.0.0E0) MR = -1 CALL CACAI(ZTA, FNU, KODE, MR, 1, CY, NN, RL, TOL, ELIM, ALIM) IF (NN.LT.0) GO TO 250 NZ = NZ + NN GO TO 120 100 CONTINUE IF (KODE.EQ.2) GO TO 110 C----------------------------------------------------------------------- C UNDERFLOW TEST C----------------------------------------------------------------------- IF (AA.LT.ALIM) GO TO 110 AA = -AA - 0.25E0*ALAZ IFLAG = 2 SFAC = 1.0E0/TOL IF (AA.LT.(-ELIM)) GO TO 180 110 CONTINUE CALL CBKNU(ZTA, FNU, KODE, 1, CY, NZ, TOL, ELIM, ALIM) 120 CONTINUE S1 = CY(1)*CMPLX(COEF,0.0E0) IF (IFLAG.NE.0) GO TO 140 IF (ID.EQ.1) GO TO 130 AI = CSQ*S1 RETURN 130 AI = -Z*S1 RETURN 140 CONTINUE S1 = S1*CMPLX(SFAC,0.0E0) IF (ID.EQ.1) GO TO 150 S1 = S1*CSQ AI = S1*CMPLX(1.0E0/SFAC,0.0E0) RETURN 150 CONTINUE S1 = -S1*Z AI = S1*CMPLX(1.0E0/SFAC,0.0E0) RETURN 160 CONTINUE AA = 1.0E+3*R1MACH(1) S1 = CMPLX(0.0E0,0.0E0) IF (ID.EQ.1) GO TO 170 IF (AZ.GT.AA) S1 = CMPLX(C2,0.0E0)*Z AI = CMPLX(C1,0.0E0) - S1 RETURN 170 CONTINUE AI = -CMPLX(C2,0.0E0) AA = SQRT(AA) IF (AZ.GT.AA) S1 = Z*Z*CMPLX(0.5E0,0.0E0) AI = AI + S1*CMPLX(C1,0.0E0) RETURN 180 CONTINUE NZ = 1 AI = CMPLX(0.0E0,0.0E0) RETURN 240 CONTINUE NZ = 0 IERR=2 RETURN 250 CONTINUE IF(NN.EQ.(-1)) GO TO 240 NZ=0 IERR=5 RETURN 260 CONTINUE IERR=4 NZ=0 RETURN END